内蒙古中部中晚二叠世构造隆升 : 来自锆石U-Pb年代学及(U-Th)/He 数据的约束

华北北缘西段及其相邻地区在中晚二叠世是否发生强烈构造隆升及其机制是区域地质研究的热点问题, 对于理解中亚造山带增生造山区与华北克拉通之间的碰撞过程具有重要意义。本文针对内蒙古达茂旗及其邻区的奥陶纪、石炭纪和中元古代侵入岩开展了锆石U-Pb 年代学和锆石(U-Th)/He 热年代学研究, 结合区域地质背景, 探讨了中晚二叠世至早侏罗世的构造隆升过程。本文研究样品包括达茂旗北部的奥陶纪辉长闪长岩(DM210)、东南部的石炭纪花岗闪长岩(DM06)以及四子王旗北部的中元古代正长花岗岩(SZ34)。锆石U-Pb 定年结果显示, 三个样品的结晶年龄分别为1338±25 Ma、458±2 Ma 和326±3 Ma。锆石 (U-Th)/He 年龄分析表明, 样品DM06 和DM210 记录了中晚二叠世(约270~250 Ma)的快速冷却事件, 而样品SZ34 则记录了早侏罗世(约180~200 Ma)的冷却事件。结合其他同类研究报道, 本文提出中晚二叠世华北拼合体系发生了整体抬升。同时, 基于古地磁、岩浆岩及沉积学等多方面证据支持的中晚二叠世古亚洲洋中段闭合的推断, 我们进一步认为上述构造抬升是由古亚洲洋闭合伴随的碰撞作用引发的挤压汇聚效应所致, 表现出与中亚造山带典型增生造山区软碰撞明显不同的特征。此外, 早侏罗世的冷却事件可视为前人提出的三叠纪末期由蒙古–鄂霍茨克洋俯冲诱发的陆内伸展相关构造抬升的延续。

Whether a significant tectonic uplift occurred on the west segment of the North China Collage System (NCCS) during the Middle and Late Permian remains ambiguous, impeding our comprehension of the collision process between the North China Craton (NCC) and the Central Asian Orogenic Belt. In this study, we conducted a detailed investigation of Proterozoic to Carboniferous intrusions in the west segment of the NCCS, specifically in the Damaoqi and Siziwangqi regions of Inner Mongolia, using zircon U-Pb and (U-Th)/He thermochronology. The samples analyzed include Ordovician gabbrodiorite (DM210),
Carboniferous granodiorite (DM06), and Mesoproterozoic orthoclase feldspar granite (SZ34). Zircon U-Pb dating yielded crystallization ages of ca. 1338±25 Ma, 458±2 Ma, and 326±3 Ma for samples DM210, DM06, and SZ34, respectively. Zircon (U-Th)/He ages indicate cooling events at ~270–250 Ma for samples DM06 and DM210, and ~200–180 Ma for sample SZ34. Combined with similar studies along the NCCS, we propose that the NCCS underwent an overall tectonic uplift during the Middle and Late Permian. Furthermore, given the Middle-Late Permian closure of the Paleo-Asian Ocean (PAO), supported by multiple lines of evidence (such as paleomagnetism, magmatic rocks, and sedimentology, etc.), we further suggest that this tectonic uplift was triggered by compression and convergence associated with the collision related to the PAO closure. Additionally, we propose that the Early Jurassic cooling event likely represents the continuation of the Late Triassic tectonic uplift in the northern NCC, previously interpreted as a response to intracontinental extension induced by the subduction of the Mongolian-Oshkosh Ocean to its north.